Over the last twelve years the continuing discovery and increasingly
accurate characterization of brown dwarfs and extrasolar giant planets
(EGPs) have created a new frontier in stellar and planetary
astronomy. The development of accurate spectral diagnostics and the
refinement of the theoretical models to describe these objects are
among the most important challenges for the future. We are
contributing to both of these goals through a combined theoretical and
experimental program to obtain highly accurate profiles of alkali
resonance lines broadened by collisions with molecular hydrogen and
helium.

Sequence of Astronomical Objects in Visible Light
(courtesy of NASA/IPAC/R. Hurt)
This figure shows an artist's rendition comparing brown dwarfs to
stars and planets. All objects are plotted to the same scale. On the
far left is the limb of the Sun. To its right is shown a very low mass
star (a so-called "late-M dwarf"), a couple of brown dwarfs (a hotter
"L dwarf" and a cooler "T dwarf"), and the planet Jupiter. These
objects have masses ranging from 1050 times that of Jupiter (for the
Sun) through 75, 65, 30, and 1 Jupiter mass for the late-M dwarf, L
dwarf, T dwarf, and Jupiter, respectively. The colors of the brown
dwarfs are chosen to match an age of 1 billion years. Despite the
range in mass, all four of the low-mass objects are approximately the
same size, ten times smaller than the diameter of the Sun.
The visible-light sequence shows how these objects might appear to the
human eye: the M and L dwarfs are red, while the T dwarf is dimly
magenta, due to lack of light -- actually absorptions by sodium and
potassium atoms -- in the green portion of the spectrum.